This invention relates generally to injection molding apparatus and a method of making it and more particularly to such apparatus and method wherein a number of cylindrical inserts each having a curved melt duct extending therethrough are each securely seated in a predetermined position in one of a plurality of spaced transverse openings extending through a melt distribution manifold.
Injection molding apparatus having a heated melt distribution manifold and a plurality of spaced heated nozzles each conveying melt to a different gate are well known. The melt distribution manifold has a melt passage with a number of branches extending outwardly from a common inlet portion to convey the melt to the spaced heated nozzles. Each nozzle has a central melt bore extending at 90.degree. to the branches of the melt passage in the melt distribution manifold. It is also known to seat inserts or plugs in transverse openings extending through the melt distribution manifold in alignment with the nozzles. Each insert has a melt duct with a smoothly curved bend extending through 90.degree. from an inlet in alignment with a respective branch of the melt passage in the melt distribution manifold to an outlet in alignment with the melt bore through an aligned nozzle.
In order to avoid color change problems and stress in the melt it is critical that the melt duct through each insert be very accurately aligned with the respective branch of the melt passage and the central melt bore through the respective nozzle. It is also important that the insert be secured in place to withstand rearward forces from the pressurized melt flowing through the bend in the melt duct. Mold-Masters Limited, Canadian Patent Application Serial Number 2,047,461 laid open Jan. 20, 1993 entitled "Injection Molding Manifold with Removable Inserts" shows inserts which are aligned by alignment pins and are tapered to withstand the force of the melt flowing through the curved melt ducts. U.S. Pat. No. 5,366,369 to Gellert which issued Nov. 22, 1994 shows inserts having outer flange portions to securely retain them in place against these same forces. However, these previous inserts have the disadvantages that they are relatively costly to make and slight misalignment remains a problem, particularly when molding some modern materials which are very shear sensitive.